Hitherto, a multi air conditioner for a building to which an air-conditioning apparatus that performs a cooling operation or a heating operation by circulating a refrigerant between an outdoor unit, which is a heat source machine arranged outside a room, and an indoor unit arranged inside the room so as to convey cooling energy or heating energy to a region to be air-conditioned such as an indoor space is applied has been present. As the refrigerant used in such an air-conditioning apparatus, HFC refrigerants, for example, are widely used. Also, a natural refrigerant such as carbon dioxide (CO2) has begun to be used.
Also, an air-conditioning apparatus of other configurations represented by a chiller system is present. In this air-conditioning apparatus, cooling energy or heating energy is generated in a heat source unit arranged outdoors, the cooling energy or heating energy is transferred to a heat medium such as water, an anti-freezing fluid by a heat exchanger arranged in the outdoor unit, and this is conveyed through a heat-medium circulation circuit to a fan coil unit, a panel heater and the like, which are an indoor unit arranged in a region to be air-conditioned, so as to perform the cooling operation or heating operation (See Patent Document 1, for example).
Among these prior-art air-conditioning apparatuses, in a prior-art air-conditioning apparatus in which a refrigerant is circulated through an indoor unit, it is likely that a user is negatively affected if the refrigerant leaks into the room. Thus, for a prior-art air-conditioning apparatus in which the refrigerant is circulated through the indoor unit, the air-conditioning apparatus that can detect leakage of the refrigerant into the room (through pipelines of a use-side heat exchanger and the vicinity of the use-side heat exchanger) has been proposed, and an air-conditioning apparatus “configured to be provided with a single heat source unit A having a compressor 1, a four-way switching valve 2 that switches a channel of a refrigerant discharged from this compressor, and a heat-source unit side heat exchanger 3, a plurality of indoor units B, C, and D having an indoor heat exchanger 5 and a flow-rate controller 9, and a relay unit having a first branch portion 10 having valve devices 8a and 8b that connect the heat source unit and the indoor unit by first and second connection pipelines 6 and 7 and also connect one end of each of the indoor heat exchangers to the first and second connection pipelines capable of being switched, a valve device 20 connected to each of the other ends of the indoor heat exchangers, respectively, and a second branch portion 11 that can connect the other ends of each of the indoor heat exchangers to the second connection pipeline through check valves 17 and 18 connected to the valve device, respectively” (See Patent Document 2, for example), for example, is proposed.    Patent Document 1: Japanese Unexamined Patent Application Publication No. 2003-343936 (page 5, FIG. 1)    Patent Document 2: Japanese Unexamined Patent Application Publication No. 2003-130482 (Abstract, FIG. 1)